JPH053376B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) This invention relates to a method for manufacturing a multilayer container made of synthetic resin and having an intermediate layer. (Prior Art) Packaging containers made of synthetic resins made by blow- or stretch-blow molding are lightweight and have drop strength, but they have inferior gas barrier properties compared to glass, and contain contents that do not like the permeation of oxygen, carbon dioxide, etc. When used as a container, further improvements were required. Therefore, a multilayer container having at least three layers has been developed, in which a resin forming the container body is provided with another resin as an intermediate layer to compensate for the defects of the resin. Furthermore, for the intermediate layer, resins such as ethylene/vinyl alcohol copolymers and polyamides, which have excellent gas barrier properties, are used. This multi-layered container can contain an extruded or injection-molded multilayer parison as well as a single-layered container.
It can be made by blow molding or stretch blow molding, with the intermediate layer being located in the middle or inside the resin forming the container body.
In a container body in which this intermediate layer is located in the center, there is no difference in the thickness of the two layers, the inner layer and the outer layer, which are defined by the intermediate layer, but if the intermediate layer is located toward the inside, , there is a difference in the thickness of the inner and outer layers,
The inner layer is significantly thinner than the outer layer. The wall thickness distribution of each layer in a multilayer container is determined by the wall thickness distribution of a multilayer bottomed parison formed by extrusion or injection molding, and the ratio of the wall thickness of the parison directly becomes the ratio of the wall thickness of the container. The molding of multi-layer bottomed parisons was carried out by the Special Publication Publication No. 59-29416.
As described in the publication, a double nozzle having an outer channel communicating with the nozzle opening and an inner channel opening at the tip of the outer channel is used to form a parison. The resin is injected into the cavity from the outer channel, and the intermediate layer forming resin is injected from the inner channel. Also, although the thickness of the intermediate layer can be changed depending on the amount of the two resins injected, the intermediate layer always forms inwardly.
As a result, the inner layer is formed thin. (Problems to be Solved by the Invention) In resins such as ethylene-vinyl alcohol copolymer (EVOH) and polyamide (PA), as the amount of moisture absorbed increases, the amount of permeation of oxygen, carbon dioxide, etc. increases. On the other hand, the biaxially oriented polyester resin used for carbonated beverage bottles has a lower moisture permeability than the above-mentioned resins, but as with all resins, the moisture permeability depends on the thickness. For this reason, in a multilayer container with a thin inner layer, even if the resin forming the container is biaxially stretched polyethylene terate, the gas barrier properties of the intermediate layer may deteriorate due to the influence of moisture absorption from the contents. The permeability of oxygen and carbon dioxide increases. For this reason, they are not suitable for long-term storage of beer and carbonated drinks, and in order to be used as containers for foods and drinks that do not allow oxygen to pass through, even multilayer containers must further improve their gas barrier properties. It is said that (Means for Solving the Problems) This invention was devised to solve the problems of the multilayer containers described above, and its purpose is to use the same resin as the conventional multilayer containers, but The amount of oxygen permeation and the amount of carbon dioxide permeation are much lower than those with conventional structures, and it goes without saying that it can maintain gas barrier properties for a long period of time, and even under relatively high temperature conditions. An object of the present invention is to provide a method for manufacturing a multilayer container. The feature of the present invention for the above-mentioned purpose is to use a double nozzle having an outer flow path communicating with a nozzle opening and an inner flow path opened within the tip of the outer flow path, and to connect the cavity from the inner flow path. A resin forming a bottomed parison is injected, and another thermoplastic resin forming an intermediate layer in relation to the resin is injected into the resin, so that the intermediate layer is biased toward the outer layer, and the intermediate layer is offset toward the outer layer. A multilayer bottomed parison of at least three layers is formed, the inner layer defined by the intermediate layer is thicker than the outer layer, and the multilayer bottomed parison is stretch blow molded to form a parison with an inner layer significantly thicker than the outer layer. The purpose is to form it into a multilayer container. (Function) In the above method, the inner layer can be formed to be significantly thicker than the outer layer within the limited wall thickness of the container. The effect of moisture absorption from the inside of the container to the intermediate layer is smaller than that of the formed one.
In addition, the gas barrier properties of the resin itself forming the inner layer are improved, so that the gas barrier properties of the multilayer container are further improved compared to conventional containers. Further, the present invention will be explained in detail with reference to Examples. (Example) Figure 1 shows a bottle-shaped multilayer container 1 with a three-layer structure as a whole.
The inner layer 11 and the outer layer 12 are made of the same thermoplastic resin, and the intermediate layer 13 is made of a thermoplastic resin with excellent gas barrier properties. The intermediate layer 13 is provided offset to the outer layer 12, so that the inner layer 11 is significantly thicker than the outer layer 12. The thickness of the inner layer 11 and the outer layer 12 is preferably an outer layer/inner layer ratio of 1:1.50 or more, and the gas barrier properties improve as the inner layer increases. The multilayer container 1 has a parison-forming resin and an intermediate layer 23 made of another resin injected into the resin.
A multilayer bottomed parison 2 with a three-layer structure partitioned into an inner layer 21 and an outer layer 22 with different wall thicknesses,
It can be manufactured by stretch blow molding. This multilayer bottomed parison 2 is injected using a double nozzle 3 that is concentrically equipped with an outer flow path 32 communicating with a nozzle opening 31 and an inner flow path 33 opened within the tip of the outer flow path 32. molded. In the conventional molding of a multilayer bottomed parison using a double nozzle, the parison-forming resin is injected into the mold 4 from the outer channel 32, but in this invention, contrary to the conventional method, the parison-forming resin is injected from the inner channel 33. The parison molding resin 5 is injected, and the intermediate layer forming resin 6 is injected from the outer channel 32. The injection into the mold 4 is as shown in FIG.
First, a suitable amount of parison molding resin 5 is injected from the inner channel 33 to begin. Next, as shown in FIG. 4, the parison molding resin 5
The injection is temporarily stopped (about 0.1 to 1.0 seconds), and the intermediate layer molding resin 6 is injected from the outer flow path 32 into the parison molding resin 5 previously injected. Thereafter, when the parison molding resin 5 is again started to be injected together with the intermediate layer molding resin 6, as shown in FIG. A multi-layer bottomed parison 2 having a three-layer structure is produced, in which the intermediate layer 23 is located biased towards the outer layer 22. Then, when the injection of the intermediate layer molding resin 6 is stopped and a small amount of the parison molding resin 5 is injected to complete the injection, the intermediate layer 23 is also encapsulated at the bottom. In the above injection molding process, an ethylene/vinyl alcohol copolymer is used as the intermediate layer molding resin. However, when forming the intermediate layer 23 of metaxylylene group-containing polyamide, the intermediate layer is The molding resin 6 is injected alone, and then the parison molding resin 5 is further injected. Even in such an injection molding process, as long as the parison molding resin 5 is injected from the inner flow path 33 and the intermediate layer molding resin is injected from the outer flow path 32, the inner layer 2
A multilayer bottomed parison 2 is produced in which the outer layer 1 is significantly thicker than the outer layer 22. Next, the gas barrier effect in a biaxially oriented three-layer container manufactured by conventional stretch blow molding of the multilayer bottomed parison 2 will be shown. Examples and Comparative Examples Container type Round bottom bottle for carbonated drinks, 0.7, 26g, Container material PET: Teijin TR-8550 PA: MXD-6 Nylon EVOH: Kuraray Eval E-105 Oxygen/carbon dioxide gas permeability coefficient (per bottle) ) cc/2Kg・24 hours・1
Barometric oxygen permeation meter MOCON, 2-unit gas permeation meter Carbon dioxide permeation meter MOCON 5-unit gas permeation meter (measures a 4-volume carbonated water filled container) Measurement conditions Relative humidity inside 100%RH, outside 65%RH , room temperature 24℃. Examples 1 and 2 and Comparative Example 1 left for one week Container composition Outer layer/middle layer/inner layer PET/MXD-6 nylon/PET

【table】 Examples 3, 4 and comparative example 2 Composition of the container Outer layer/middle layer/inner layer PET EVOH PET

【table】

[Table] (Effects of the Invention) In this invention, the intermediate layer is shifted toward the outer layer, the inner layer is significantly thicker than the outer layer, and this thickness improves the gas barrier properties of the inner layer. This reduces moisture permeability from the contents side, prevents deterioration of the gas barrier properties of the intermediate layer due to moisture absorption, and provides even better gas barrier properties, making it suitable for packaging containers for beer and carbonated drinks. When used as a container, the storage period of the contents can be extended, and the range of uses is further expanded, as it can also be used for containers for ketchup and apple juice, which were previously used due to oxygen permeability issues. . Also, no special molding technology is required for manufacturing.
Since it can be easily manufactured using conventional equipment and molding techniques, it has the advantage of not being particularly expensive.

[Brief explanation of the drawing]

FIG. 1 is a partially enlarged partial sectional view of a multilayer container manufactured by the manufacturing method of the present invention, FIG. 2 is a partial sectional view of a multilayer bottomed parison, and FIGS. FIG. 3 is a schematic cross-sectional view sequentially showing the steps of forming the bottom parison. 1...Multilayer container, 2...Multilayer bottomed parison, 3
...Double nozzle, 5...Parison molding resin, 6...
...Intermediate layer molding resin, 11...Inner layer, 12...Outer layer, 21...Inner layer, 22...Outer layer, 23...Intermediate layer, 31...Nozzle opening, 32...Outer channel, 33
...Inner flow path.

Claims (1)

[Claims] 1 having an outer flow path communicating with the nozzle opening and an inner flow path opening within the tip of the outer flow path;
Using a heavy nozzle, a resin forming a bottomed parison is injected into the cavity from the inner channel, and another thermoplastic resin forming an intermediate layer in relation to the resin is injected into the resin to form an intermediate layer. Molding a multilayer bottomed parison with at least three layers in which the layers are offset toward the outer layer and the inner layer defined by the intermediate layer is thicker than the outer layer, and stretch blow molding the multilayer bottomed parison. A method for manufacturing a multilayer container, characterized in that the inner layer is significantly thicker than the outer layer.